1. Field of the Invention
The invention relates generally to apparatuses and processes for digesting cellulosic material. In particular, the invention relates to cellulosic digestion apparatuses and processes that involve a means for distributing pressurize digestion fluid to increase cellulosic digestion efficiency, an improved sealing assembly, and/or an improved fluid flow transporting design that leads to systemic longevity.
2. Description of Background Art
Paper manufacturing typically requires digestion of a cellulosic material, e.g., wood chips. For example, a cellulosic digestion process may involve impregnating wood chips with fresh cooking liquor (white liquor) and then placing the impregnated chips in a digesting apparatus where they may be heated to cooking temperature. Once cooked down, the cellulosic material is digested and converted into pulp. To create white paper, the pulp is typically then washed, refined, further delignified, and bleached using any of a number of oxidizing agents, e.g., chlorine-based or other high strength oxidizers.
There is a substantial current need for improved pulping apparatuses adaptable to produce paper pulp and/or intermediate fibrous materials rapidly and in high yields. Such apparatuses may be used to produce pulp from a wide variety of cellulosic materials and may be designed to carry out cellulosic digestion in batch or continuous processes. In a conventional batch cooking sulfite process, for example, a digester is filled with wood chips and charged with fresh cooking liquor. The digester is then sealed, and heated to cooking temperature by direct or indirect heating. Once cooked, a substantial portion of the lignin and carbohydrates may be degraded and/or leached from the pulp. Spent cooking liquor (black liquor) and the pulp are separated after cooking.
The laboratory digester is one of the most widely used instruments in the pulp and paper industry. The digester allows a user to experiment with a wide range of chemical compositions in order to optimize the full-scale cooking process. Laboratory digesters are available in a wide range of volumes and may provide critical insight into the chip cooking process for scale-up and/or optimization efforts.
A number of laboratory digesters are commercially available. For example, M/K Systems, Inc. (Bethesda, Md.) manufactures a high-pressure batch process digester that runs pulp-digesting processes on a laboratory scale in a controlled precise manner. Available in both single and dual vessel models, the digester provides excellent control over the cooking profile as well as homogeneous temperature distribution due to excellent systemic flow control. In addition, the digester is suitable for both alkaline and acid digesting process with various types of wood chips and fiber sources. Furthermore, the digester is designed to operate at high temperatures at an elevated pressure, i.e., up to about 300 PSI.
Nevertheless, there exist opportunities to provide alternatives and improvements to cellulosic digestion technologies, particularly to overcome any shortcomings associated with known cellulose digesters. For example, improvements may be made in the areas of digestion efficiency and quality. In addition, improved sealing and fluid-transportation technologies may enhance the safety, convenience, and corrosion associated with the operation of high-pressure digesters.